A commonly used process for the determination of amino acid sequences in proteins is disclosed by P. Edman and G. Begg, European Journal of Biochemistry, Vol. 1, 1967, pages 80-91. In this process, which is based upon the degradation of phenylisothiocyanate, the free N-terminal alpha-amino group of a protein is first converted into a phenylthiocarbamyl (PTC) derivative through coupling with phenylisothiocyanate (PITC) in a basic environment. The phenylthiocarbamyl derivative is cleaved in a strongly acidic environment and is cyclized through formation of a thiazolinone derivative (ATZ), which then can be converted by treatment with aqueous acid into the more stable phenylthiohydantoin (PTH) derivative. The alpha-amino group of the next in the chain of amino acids is thus set free and can be subjected to a further degradation. The PTH amino acid can be identified by using liquid chromatography.
EP-A-279882 discloses one apparatus which can be used for automatically sequencing proteins according to the above-described degradation scheme. The disclosed apparatus comprises a cup-shaped reactor vessel which spins around its longitudinal axis, and a movable pipette which connects with a syringe such that liquid can be sucked into or expelled from the pipette. The movable pipette is used to deposit various reagents and solvents on the wall of the spinning reactor vessel, where they come into contact with a sample of, for example, proteins or peptides to be sequenced. The movable pipette is also used for removing reaction products and excess products from the reactor vessel. Due to the high rotation speed of the reactor vessel (typically several hundred revolutions per minute), special designs regarding drive and bearing of the reactor vessel are required.
It is accordingly one object of the present invention to provide an apparatus for processing liquid which has a simpler design and which avoids the problems associated with a spinning reactor vessel.